Real-time PostgreSQL: Pick approach for roll-up tables and implement

[ozgune]

PostgreSQL can easily be extended to create aggregate tables as raw data gets ingested into the database.

We explored several methods to create roll-up tables and also presented a tutorial on it. We could evaluate our learnings from this tutorial and pick and implement an approach: https://www.youtube.com/watch?v=0ybz6zuXCPo

[sumedhpathak]

Noted by @samay-sharma as a frequent customer requested issue.

[onderkalaci]

@ozgune Do we still need to keep this issue open?

[marcocitus]

Various articles on how to create aggregate tables in Citus:
https://www.citusdata.com/blog/2018/06/14/scalable-incremental-data-aggregation/
https://www.citusdata.com/blog/2017/12/27/real-time-analytics-dashboards-with-citus/
https://www.citusdata.com/blog/2016/11/29/event-aggregation-at-scale-with-postgresql/